CN102959425A - Magnetic resonance imaging using steering-propeller - Google Patents

Abstract

A GRASE-type PROPELLER sequence called Steer-PROP is disclosed. This sequence exploits a serious of steer blips together with rewinding gradient pulse to traverse k-space. Steer-PROP improves the scan time by a factor of 3 or higher compared to FSE- PROPELLER, provides improved robustness to off-resonance effects compared to EPI- PROPELLER, and addresses a long-standing phase correction problem inherent to GRASE based sequences. Steer-PROP also enables intra-blade, inter-blade, and inter-shot phase errors to be separately determined and independently corrected.

Description

Use the magnetic resonance imaging of screw-rudder technology

The cross reference of related application

The application requires the right of priority of the U.S. Provisional Application 61/29,203 of submission on April 29th, 2010, by reference it is incorporated herein at this.

Background technology

Magnetic resonance imaging (MRI) is usually used in imaging subject's interior tissue.MRI usually subject or the object by will imaging is placed on the uniform strong magnetic field B that is called main field ₀Isocenter on or near carry out.Main field makes in the material that forms subject or object has the atomic nucleus (spin) of magnetic moment along the magnetic field in-line arrangement.This spin forms the magnetization that centers on the magnetic direction precession with the speed that is directly proportional with magnetic field intensity.For proton (the common nuclear that adopts in MRI), precession frequency is about 64 megahertzes (MHz) in the magnetic field of 1.5 teslas.If the magnetization is subject to being called B ₁The little radio-frequency (RF) magnetic field disturbance in magnetic field, then spin can be sent radio frequency (RF) radiation with characteristic frequency.The RF radiation of can determination and analysis sending is to draw the information of the image that can be used for generating subject or object.With regard to the discussion of this paper, when describing the magnetic resonance imaging of " object ", term " object " will be used in reference to subject (for example, people) or object (for example, tested object).

In practice, except main field, also magnetic field gradient is applied to subject or object.Magnetic field gradient is used along one or more orthogonal axes (x, y, z) usually, and the z axle usually and B ₀Unanimously, and cause frequency and/or the phase space changes in distribution of precession nuclear spin.By using radio frequency B with the well-designed pulse and/or the pulse train that switch on and off ₁Magnetic field and gradient magnetic, the RF radiation of sending can carry when detected and when analyzing, can be used for generating subject or object in detail, the space encoding information of high-definition picture.People have developed the various technology of utilizing specific sequence of pulses and advanced image rebuilding method, and new progress is provided, but have also brought new challenge.

Single-shot echo planar image (ss-EPI) is the popular pulse train of using for the many fast imagings as functional imaging, Diffusion Imaging and Perfusion Imaging.Except the robustness and high data acquisition efficient of its anti-motion, ss-EPI also has the low specific absorption rate (SAR) that the High-Field imaging is wished especially.Yet along with the expanded range of advanced imaging, the limitation of ss-EPI is more and more obvious.Except it was extremely sensitive to magnetic susceptibility variation and eddy current, the use of single-shot had restricted maximum k spatial coverage, and this has greatly reduced can reach spatial resolution.This problem strengthens along with magnetic field and becomes more outstanding, because the T2* relaxation time that shortens makes the available sampling windows narrow.

The common way that reaches high spatial resolution is to adopt repeatedly excitation pulse sequence.Except improving resolution, repeatedly excite EPI also to reduce magnetic susceptibility artifact and eddy current susceptibility.Main deficiency is that the susceptibility of moving has been increased.A kind of effective means that solves motion problems is the overlapping parallel lines of Periodic Rotating (PROPELLER, the screw propeller) sampling policies (1) of strengthening rebuilding to be incorporated into repeatedly excite among the EPI.The people's such as Chung preliminary realization is along the minor axis designated phase coding staff of PROPELLER blade (blade) to (2).Because it is still slow along phase-encoding direction to pass through the speed (dk/dt) in k space, so the off-resonance effect in each blade still causes obvious pseudo-shadow.Recently, the people such as Skare has been developed the Different Strategies (3) that phase-encoding direction is switched to " minor axis " from " major axis " of PROPELLER blade.This design has significantly increased the bandwidth of phase encoding, thereby has reduced the distortion of image.Yet the phenomenon all there is off-resonance effect in which kind of realization and is called " gradient anisotropy " (4) was observed in inclination EPI obtains (5-7) originally.

Rely on its immunity to off-resonance effect, FSE or whirlpool formula spin echo (TSE) have been widely used in clinical.Many repeatedly the exciting in the FSE technology of developing in the time of two more than ten years in the past utilizes the FSE of PROPELLER sampling to absorb in recent years a large amount of concern (8).Except inherit the desired characteristic of getting off from FSE, PROPELLER-FSE is owing to its intrinsic over-sampling around k space, center provides effective auto-navigation.But, compare with EPI-PROPELLER pulse train, FSE-PROPELLER will be slowly many.

Summary of the invention

Embodiment disclosed herein provides based on the PROPELLER pulse train of gradient and has utilized new k space to pass through the spin echo PROPELLER(GRASP of strategy and comprehensive phase correction scheme) sequence, in order to comparing the shortening data acquisition with FSE-PROPELLER during the time, obtain the image that pseudo-shadow is extremely not obvious or do not have.The present invention further comprises the identification that usually involves former method and can separate the dissimilar phase error of proofreading and correct with independence for the k spatial data that uses GRASP retrieval disclosed herein.

Therefore, in one aspect, various embodiment of the present invention provides in magnetic resonance imaging (MRI) system and has comprised following computer implemented method: with the object of the first radio frequency (RF) pulse application in the MRI system, and between the first fast spin echo (FSE) echo after the time interval, with the 2nd RF pulse application in this object; During the time interval between the FSE echo between the first and second RF pulses along first direction with the first magnetic field gradient (G _x) spike train is applied to this object, a G _xSpike train comprises integer M adjacent G _xPulse, a G _xEvery couple of G in succession of spike train _xPulse is by G _xTurn to pulse separately, and a G _xThe last G of spike train _xThe pulse back is a G then _xThe wraparound pulse; With a G _xSpike train side by side along second direction with the first magnetic field gradient (G _y) spike train is applied to this object, a G _ySpike train comprises M adjacent G _yPulse, a G _yEach G of spike train _yPulse and a G _xCorresponding G in the time of spike train _xThe corresponding first row G of pulse shaping _x-G _yPulse pair, a G _yEvery couple of G in succession of spike train _yPulse is by G _yTurn to pulse separately, this G _yTurn to pulse and a G _xCorresponding G in the time of spike train _xTurn to the corresponding first row G of pulse shaping _x-G _yTurn to pulse pair and a G _yThe last G of spike train _yThe pulse back is a G then _yThe wraparound pulse, a G _yWraparound pulse and a G _xThe one G of spike train _xWraparound pulse shaping first is G simultaneously _x-G _yWraparound pulse pair; Obtain the k spatial data along the first group of mutual angled straight lines of M bar that intersects in the center in k space, each bar of first group the mutual angled straight lines of M bar is corresponding to different corresponding first row G _x-G _yEach first row G is wherein used in pulse pair _x-G _yTurn to pulse that starting point that the k space is passed through is reoriented to another from one of mutual angled straight lines of M bar of first group, and wherein use the first G simultaneously _x-G _yThe wraparound pulse is reoriented to the reference location in k space to the starting point that the k space is passed through.

In one aspect of the method, various embodiment of the present invention provides in magnetic resonance imaging (MRI) system and comprised following computer implemented method: the first gradient and spin echo screw propeller (GRASP) pulse train are applied to object in the MRI system, and this first gradient and spin echo screw propeller (GRASP) pulse train comprises the first radio frequency (RF) sequence of periodically RF pulse, along the periodicity G of first direction _xSpike train follow the first magnetic field gradient (G _x) sequence and along the periodicity G of second direction _ySpike train follow corresponding the first magnetic field gradient (G _y) sequence, a RF, G _xAnd G _ySequence is configured to make passing through along more than first parallel lines grouping in the k space, each parallel lines grouping of more than first forms a corresponding GRASP blade, and each corresponding GRASP blade tilts with respect to other corresponding GRASP blades, and a GRASP blade corresponding to other intersects in the center in k space; A GRASP k spatial data is therefrom obtained in parallel lines grouping along more than first during first repetition interval corresponding with the duration of a GRASP pulse train; The 2nd GRASP pulse train is applied to this object, and the 2nd GRASP pulse train comprises the 2nd RF sequence, the periodicity G of periodically RF pulse _xSpike train follow the 2nd G _xSequence and periodicity G _ySpike train follow corresponding the 2nd G _ySequence, the 2nd RF, G _xAnd G _ySequence is configured to make passing through along more than second parallel lines grouping in the k space, each parallel lines grouping of more than second forms corresponding the 2nd GRASP blade, and each corresponding the 2nd GRASP blade tilts with respect to other corresponding the 2nd GRASP blades, and two GRASP blade corresponding to other intersects in the center in k space; The 2nd GRASP k spatial data is therefrom obtained in parallel lines grouping along more than second during second repetition interval corresponding with the duration of the 2nd GRASP pulse train; And separately determine and independent the correction: the phase error in the GRASP k spatial data that (i) obtains between the parallel lines of each corresponding GRASP blade, phase error in the GRASPk spatial data that (ii) obtains between the corresponding GRASP blade, phase error in the 2nd GRASP k spatial data that (iii) obtains between the parallel lines of each corresponding the 2nd GRASP blade, phase error in the 2nd GRASP k spatial data that (iv) obtains between corresponding the 2nd GRASP blade, the and (phase error in a GRASP who v) obtains between a GRASP pulse train and the 2nd GRASP pulse train and the 2nd GRASP k spatial data.

In a further aspect, various embodiment of the present invention provides and has comprised following MRI system: one or more processors; Storer; Main magnet; Be placed on a plurality of gradient coils in this main magnet; The RF transceiver system; The RF coil block; Signal is sent to the pulse module of this RF coil block; Be subjected to the RF switch of this pulse module control; And be stored in machine readable instructions in this storer, this machine readable instructions is when being carried out by these one or more processors, make this MRI system realize comprising following function: with the object of the first radio frequency (RF) pulse application in this MRI system, and between the first fast spin echo (FSE) echo after the time interval, with the 2nd RF pulse application in this object; During the time interval between the FSE echo between the first and second RF pulses along first direction with the first magnetic field gradient (G _x) spike train is applied to this object, a G _xSpike train comprises integer M adjacent G _xPulse, a G _xEvery couple of G in succession of spike train _xPulse is by G _xTurn to pulse separately, and a G _xThe last G of spike train _xThe pulse back is a G then _xThe wraparound pulse; With a G _xSpike train side by side along second direction with the first magnetic field gradient (G _y) spike train is applied to this object, a G _ySpike train comprises M adjacent G _yPulse, a G _yEach G of spike train _yPulse and a G _xCorresponding G in the time of spike train _xThe corresponding first row G of pulse shaping _x-G _yPulse pair, a G _yEvery couple of G in succession of spike train _yPulse is by G _yTurn to pulse separately, this G _yTurn to pulse and a G _xCorresponding G in the time of spike train _xTurn to the corresponding first row G of pulse shaping _x-G _yTurn to pulse pair and a G _yThe last G of spike train _yThe pulse back is a G then _yThe wraparound pulse, a G _yWraparound pulse and a G _xThe one G of spike train _xWraparound pulse shaping first is G simultaneously _x-G _yWraparound pulse pair; Obtain the k spatial data along the first group of mutual angled straight lines of M bar that intersects in the center in k space, each bar of first group the mutual angled straight lines of M bar is corresponding to different corresponding first row G _x-G _yEach first row G is wherein used in pulse pair _x-G _yTurn to pulse that starting point that the k space is passed through is reoriented to another from one of mutual angled straight lines of M bar of first group, and wherein use the first G simultaneously _x-G _yThe wraparound pulse is reoriented to the reference location in k space to the starting point that the k space is passed through.

In aspect another, various embodiment of the present invention provide and have comprised following MRI system: one or more processors; Storer; Main magnet; Be placed on a plurality of gradient coils in this main magnet; The RF transceiver system; The RF coil block; Signal is sent to the pulse module of this RF coil block; Be subjected to the RF switch of this pulse module control; And be stored in machine readable instructions in this storer, this machine readable instructions is when being carried out by these one or more processors, make this MRI system realize comprising following function: the first gradient and spin echo screw propeller (GRASP) pulse train are applied to object in the MRI system, and this first gradient and spin echo screw propeller (GRASP) pulse train comprises the first radio frequency (RF) sequence of periodically RF pulse, along the periodicity G of first direction _xSpike train follow the first magnetic field gradient (G _x) sequence and along the periodicity G of second direction _ySpike train follow corresponding the first magnetic field gradient (G _y) sequence, a RF, G _xAnd G _ySequence is configured to make passing through along more than first parallel lines grouping in the k space, each parallel lines grouping of more than first forms a corresponding GRASP blade, and each corresponding GRASP blade tilts with respect to other corresponding GRASP blades, and a GRASP blade corresponding to other intersects in the center in k space; A GRASP k spatial data is therefrom obtained in parallel lines grouping along more than first during first repetition interval corresponding with the duration of a GRASP pulse train; The 2nd GRASP pulse train is applied to this object, and the 2nd GRASP pulse train comprises the 2nd RF sequence, the periodicity G of periodically RF pulse _xSpike train follow the 2nd G _xSequence and periodicity G _ySpike train follow corresponding the 2nd G _ySequence, the 2nd RF, G _xAnd G _ySequence is configured to make passing through along more than second parallel lines grouping in the k space, each parallel lines grouping of more than second forms corresponding the 2nd GRASP blade, and each corresponding the 2nd GRASP blade tilts with respect to other corresponding the 2nd GRASP blades, and two GRASP blade corresponding to other intersects in the center in k space; The 2nd GRASP k spatial data is therefrom obtained in parallel lines grouping along more than second during second repetition interval corresponding with the duration of the 2nd GRASP pulse train; And separately determine and independent the correction: the phase error in the GRASP k spatial data that (i) obtains between the parallel lines of each corresponding GRASP blade, phase error in the GRASP k spatial data that (ii) obtains between the corresponding GRASP blade, phase error in the 2nd GRASP k spatial data that (iii) obtains between the parallel lines of each corresponding the 2nd GRASP blade, phase error in the 2nd GRASP k spatial data that (iv) obtains between corresponding the 2nd GRASP blade, the and (phase error in a GRASP who v) obtains between a GRASP pulse train and the 2nd GRASP pulse train and the 2nd GRASP k spatial data.

In a further aspect, various embodiment of the present invention provides and has contained the non-of short duration computer-readable medium of storing superincumbent instruction, this instruction is in case by one or more processors execution of MRI system, just make this MRI system realize comprising following function: one or more processors; Storer; The boring magnet; Center on a plurality of gradient coils of the boring placement of this magnet; The RF transceiver system; The RF coil block; Signal is sent to the pulse module of this RF coil block; Be subjected to the RF switch of this pulse module control; And be stored in machine readable instructions in this storer, this machine readable instructions is when being carried out by these one or more processors, make this MRI system realize comprising following function: with the object of the first radio frequency (RF) pulse application in this MRI system, and between the first fast spin echo (FSE) echo after the time interval, with the 2nd RF pulse application in this object; During the time interval between the FSE echo between the first and second RF pulses along first direction with the first magnetic field gradient (G _x) spike train is applied to this object, a G _xSpike train comprises integer M adjacent G _xPulse, a G _xEvery couple of G in succession of spike train _xPulse is by G _xTurn to pulse separately, and a G _xThe last G of spike train _xThe pulse back is a G then _xThe wraparound pulse; With a G _xSpike train side by side along second direction with the first magnetic field gradient (G _y) spike train is applied to this object, a G _ySpike train comprises M adjacent G _yPulse, a G _yEach G of spike train _yPulse and a G _xCorresponding G in the time of spike train _xThe corresponding first row G of pulse shaping _x-G _yPulse pair, a G _yEvery couple of G in succession of spike train _yPulse is by G _yTurn to pulse separately, this G _yTurn to pulse and a G _xCorresponding G in the time of spike train _xTurn to the corresponding first row G of pulse shaping _x-G _yTurn to pulse pair and a G _yThe last G of spike train _yThe pulse back is a G then _yThe wraparound pulse, a G _yWraparound pulse and a G _xThe one G of spike train _xWraparound pulse shaping first is G simultaneously _x-G _yWraparound pulse pair; Obtain the k spatial data along the first group of mutual angled straight lines of M bar that intersects in the center in k space, each bar of first group the mutual angled straight lines of M bar is corresponding to different corresponding first row G _x-G _yEach first row G is wherein used in pulse pair _x-G _yTurn to pulse that starting point that the k space is passed through is reoriented to another from one of mutual angled straight lines of M bar of first group, and wherein use the first G simultaneously _x-G _yThe wraparound pulse is reoriented to the reference location in k space to the starting point that the k space is passed through.

In aspect another, various embodiment of the present invention provides and has contained the non-of short duration computer-readable medium of storing superincumbent instruction, this instruction is in case by one or more processors execution of MRI system, just make this MRI system realize comprising following function: one or more processors; Storer; The boring magnet; Center on a plurality of gradient coils of the boring placement of this magnet; The RF transceiver system; The RF coil block; Signal is sent to the pulse module of this RF coil block; Be subjected to the RF switch of this pulse module control; And be stored in machine readable instructions in this storer, this machine readable instructions is when being carried out by these one or more processors, make this MRI system realize comprising following function: the first gradient and spin echo screw propeller (GRASP) pulse train are applied to object in the MRI system, and this first gradient and spin echo screw propeller (GRASP) pulse train comprises the first radio frequency (RF) sequence of periodically RF pulse, along the periodicity G of first direction _xSpike train follow the first magnetic field gradient (G _x) sequence and along the periodicity G of second direction _ySpike train follow corresponding the first magnetic field gradient (G _y) sequence, a RF, G _xAnd G _ySequence is configured to make passing through along more than first parallel lines grouping in the k space, each parallel lines grouping of more than first forms a corresponding GRASP blade, and each corresponding GRASP blade tilts with respect to other corresponding GRASP blades, and a GRASP blade corresponding to other intersects in the center in k space; A GRASP k spatial data is therefrom obtained in parallel lines grouping along more than first during first repetition interval corresponding with the duration of a GRASP pulse train; The 2nd GRASP pulse train is applied to this object, and the 2nd GRASP pulse train comprises the 2nd RF sequence, the periodicity G of periodically RF pulse _xSpike train follow the 2nd G _xSequence and periodicity G _ySpike train follow corresponding the 2nd G _ySequence, the 2nd RF, G _xAnd G _ySequence is configured to make passing through along more than second parallel lines grouping in the k space, each parallel lines grouping of more than second forms corresponding the 2nd GRASP blade, and each corresponding the 2nd GRASP blade tilts with respect to other corresponding the 2nd GRASP blades, and two GRASP blade corresponding to other intersects in the center in k space; The 2nd GRASP k spatial data is therefrom obtained in parallel lines grouping along more than second during second repetition interval corresponding with the duration of the 2nd GRASP pulse train; And separately determine and independent the correction: the phase error in the GRASP k spatial data that (i) obtains between the parallel lines of each corresponding GRASP blade, phase error in the GRASP k spatial data that (ii) obtains between the corresponding GRASP blade, phase error in the 2nd GRASP k spatial data that (iii) obtains between the parallel lines of each corresponding the 2nd GRASP blade, phase error in the 2nd GRASP k spatial data that (iv) obtains between corresponding the 2nd GRASP blade, the and (phase error in a GRASP who v) obtains between a GRASP pulse train and the 2nd GRASP pulse train and the 2nd GRASP k spatial data.

By suitably reading with reference to the accompanying drawings following detailed description, these and other aspect, advantage and to substitute be apparent for the person of ordinary skill of the art.And, should be understood that this summary and other descriptions provided herein and figure only are intended to like this, may have many variants by the present invention of example illustration.

Description of drawings

Fig. 1 illustration pass through an embodiment of exemplary the turning in k space-PROP method;

Fig. 2 (a, b) be turn to-spin echo of PROP between fragment (a) and the corresponding k space schematic illustration of passing through (b);

Fig. 3 illustration the turning to of 3 gtadient echos of each spin echo-PROP sequence is shown and the correspondence between them turns to-fragment of tip (Steer-blip) pulse;

Fig. 4 illustration illustrate by blade 1(a), 2(b) and the tip of k space transition 3(c) design;

Fig. 5 illustration the distribution of echo in the leap k space of view ordering is shown;

Fig. 6 illustration be used for the embodiment of exemplary the turning to of phase error correction-PROP method;

Fig. 7 compared use respectively FSE-PROP(a) and the mirage phantom (phantom image) that turns to-PROP(b) obtain at 3T;

Fig. 8 (a-f) illustration for single-shot EPI(a, d relatively), FSE-PROP(b, e) and turn to-PROP(c, f) T2(a that obtains at 3T, b, c) and disperse (b=500s/mm ²) (c, d, e) weighting volunteer image;

Fig. 9 (a-c) illustration use (a) FSE, (b) FSE-PROP and (c) turn to-volunteer that PROP obtains be scheduled to the T2 image of head athletic performance;

Figure 10 (a-d) illustration use FSE-PROP(a, c) and turn to-PROP(b, d) and TR=4s and TE=72ms the T2(a, the b that obtain at 1.5T) and disperse (b=750s/mm ²) (c, d) weighting volunteer image; And

Figure 11 (a-f) illustration on axially (a, e), sagittal (b, f), crown (c, g) and inclination (d, h) plane from turn to-PROP(a-d) and SS-EPI(e-h) the diffusion-weighted image that obtains.

Embodiment

This paper provides the exemplary technique that can be applicable in the MRI system by the disclosed embodiment of example.This MRI system comprises some hardware componenies usually, and this hardware component comprises a plurality of gradient coils, the RF transceiver system of placing around the boring of magnet and is subjected to pulse module control that the RF signal is sent to the RF coil block and receives the RF switch of RF signal from the RF coil block.The RF signal that receives is also referred to as magnetic resonance (MR) signal data.The MRI system also comprises the computing machine that has been programmed to following effect: make system that various RF signals, magnetic field and magnetic field gradient are applied to the object in the system and excite and space encoding in order to cause spin in object, process the MR signal data, and the MR image that makes up object the MR signal data after processing.This computing machine can comprise the storer of one or more universal or special processors, one or more formation and with other hardware componenies handing-over of MRI system and/or control their one or more hardware and/or software interface.

The MR signal data that detects from object is described as " k space " data with mathematical term usually.The k space is the contrary space of the Fourier of image space.Image in the real space generates by Fourier transform k spatial data.The MR signal data obtains by pass through the k space in the process that various RF pulses and magnetic field gradient is applied to object.In practice, the technology of obtaining the MR signal data from object is closely related with the technology that various RF pulses and magnetic field gradient is applied to object.Example embodiment disclosed herein relates to and RF pulse and magnetic field gradient be configured to realize in advantageous particularly mode as data acquisition and/or cause that the k space passes through.And, this example embodiment can realize with the form of one or more computer programs or application program, this computer program or application program by computing machine (are for example worked as, when one or more processors) carrying out, make the various RF pulses of MRI system applies and magnetic field gradient, advantageous manner with regulation passes through the k space, and obtains corresponding MR signal data.

More particularly, this example embodiment provides and has surpassed employing based on the certain benefits of the k space crossing technology of the strategy of PROPELLER method.With repeatedly exciting fast spin echo (FSE) pulse train to realize, PROPELLER method (1) is used around the series of rectangular bar of k space initial point rotation and is passed through the k space at first.Each spin echo in the FSE echo row is used for obtaining the k spatial data of a line, and therefore whole echo row produce the blade that is comprised of the parallel k space line of N bar or rectangular, and wherein N equals echo row length (ETL).Repetition subsequently (or " TR ") involves frequency and phase encoding gradient around the rotation of section chosen axis, produces additional blades in the k space, and each additional blades has rotated certain angle to cover the complete circle district in k space more.K space center district samples by each blade, makes the auto-navigation can compensating motion.Motion correction can pass through according to the data in the overlay region, center in the plane, and ground of each blade rebuilds a series of low resolution phase diagrams and carries out.Give the motion of fixed blade cause phase error by with phase place with compare to assess with reference to the phase place of blade, during image reconstruction, eliminated subsequently.Although PROPELLER has the robustness of anti-motion in some application as human brain disperse research, it is unrealistic that the required time of high-resolution imaging may be grown.

Gradient and spin echo (GRASE) are to make the FSE that can be applied to PROPELLER of shortening sweep time and the mixture of EPI.A kind of such technology is called as " whirlpool formula screw propeller " (9), and it has increased the width of blade, thereby has improved the immunity to motion correction, because the mass of redundancy data in the k space center district can be for assessment of data consistency.The formula screw propeller scanning of each whirlpool all is comprised of a plurality of parallel blades that are combined into single wider blade.But, make that phase error complicates between blade, be not easy to solve.

More particularly, if Carr-Purcell-Meiboom-Gill(CPMG) condition is not being met, and then may have phase place inconsistent (10) between spin echo signal.In addition, mainly due to the change in polarity of readout gradient, between gtadient echo, also may there be phase error.

By passing through the k space of GRASE sequence to produce the mode that intersects and overlap near a plurality of mutual dihedral vanes the initial point (center) in k space, can advantageously separate and independent correction blade between phase error.In order to realize the crossing blade of such inclination within the single repetition time of GRASE sequence (TR), k passes through in the space and need to " turn to " another blade from a blade exciting in (that is, each TR) of sequence at every turn.This can realize by specific gtadient echo spike train of design in each of a plurality of spin echoes of GRASE sequence.As disclosed herein, this technology is called as " turning to-PROP ", and corresponding sequence is called as " gradient and spin echo screw propeller (GRASP) ".Except can making favourable phase error correction, compare with original PROPELLER technology (1), turn to-PROP also further significantly shortened the time of sampling k spatial data.

1. turn to-PROP principle and example embodiment

Turn to-PROP with each excite after the RF pulse N RF again focusing pulse produce the CPMG spin echo and be listed as.By bipolar readout gradient each spin echo is further resolved into M gtadient echo.For instance, N can be in the scope of 4-64, and M can be in the scope of 3-7, but also can use the numerical value of other M and/or N.Turn to-PROP adopts the series of prongs gradient pulse that M gtadient echo distributed to M different leaves.Like this, M blade of sampling at every turn the exciting of sequence (that is, each TR).

In Fig. 1 illustration turn to-example embodiment of PROP method.For instance, this exemplary method can be the computer implemented method in above-mentioned MRI system the sort of.

As illustrated in Fig. 1, in step 102, after exciting radio frequency (RF) pulse, with the object of a RF pulse application in the MRI system, and between the first fast spin echo (FSE) echo after the time interval, with the 2nd RF pulse application in this object.

In step 104, between the FSE echo between the first and second RF pulses in the time interval, along first direction with the first magnetic field gradient (G _x) spike train is applied to this object.The one G _xSpike train comprises integer M adjacent G _xPulse, and a G _xThe in succession paired G of spike train _xPulse is by G _xTurn to pulse separately.The one G _xThe last G of spike train _xThe pulse back is a G then _xThe wraparound pulse.

In step 106, along second direction with the first magnetic field gradient (G _y) spike train is applied to this object.The one G _ySpike train comprises M adjacent G _yPulse, a G _yThe in succession paired G of spike train _yPulse is by G _yTurn to pulse separately.The one G _yThe last G of spike train _yThe pulse back is a G then _yThe wraparound pulse.The one G _yEach G of spike train _yPulse and a G _xCorresponding G in the time of spike train _xThe corresponding first row G of pulse shaping _x-G _yPulse pair.In addition, each G _yTurn to pulse and a G _xCorresponding G in the time of spike train _xTurn to the corresponding first row G of pulse shaping _x-G _yTurn to pulse pair and a G _yWraparound pulse and a G _xThe one G of spike train _xWraparound pulse shaping first is G simultaneously _x-G _yWraparound pulse pair.

At last, in step 108, obtain the k spatial data along the first group of mutual angled straight lines of M bar that intersects in the center in k space, wherein each bar of first group the mutual angled straight lines of M bar is corresponding to the corresponding first row G of difference _x-G _yPulse pair.

According to this example embodiment, use G _xFirst direction and use G _yFirst direction mutually orthogonal.

According to this example embodiment, use each first row G _x-G _yTurn to pulse that starting point that the k space is passed through is reoriented to another from one of mutual angled straight lines of M bar of first group.In addition, use the first while G _x-G _yThe wraparound pulse is reoriented to the reference location in k space to the starting point that the k space is passed through.For instance, M can be in the scope of 3-7, but also can use the numerical value outside this scope.

Further according to this example embodiment, the first and second pulses are again focusing pulses of RF, at first cause spin echo.Magnetic field gradient pulse G _xAnd G _yEach cause gtadient echo.Get M=3 as an example, in the first and second RF again the first spin echo interval between the focusing pulse, generate three gtadient echos.Second again focusing pulse cause the second spin echo.

Should understand, turn to-PROP also can be embodied in the non-of short duration computer-readable medium as disk, CD-ROM etc., stored the non-of short duration computer-readable medium of computer executable program above comprising, if this computer executable program is carried out by one or several processor of MRI system, make the MRI system carry out the function of aforesaid exemplary method.Will also be appreciated that and can revise or rearrange above-mentioned method step, and add additional step, these do not change example embodiment or other turn to-scope or the spirit of PRO embodiment, and for example, the above is described as right G _xAnd G _yPulse (comprise and turning to and the wraparound pulse) can need not strictly to use simultaneously.In certain embodiments, G _xAnd G _yThe designing institute official hour relation of spike train is to make paired pulse simultaneously approximate rather than simultaneously strict.

A. turn to

Fig. 2 a illustration the G of M=3 _xAnd G _ySpike train and Fig. 2 b illustration pass through along the as a result k space of three blades.Be shown as three trapezoidal gradient lobe corresponding to three blades each obtain the k spatial data.Note a G _yDo not exist on the surface of pulse in fact corresponding to zero pulse height.Turn to pulse to be shown as triangle (but also can use other shapes of the gradient pulse) and to be called as turning to tip.They are used for the k space orbit is redirect to desired blade.Triangle gradient pulse on the end of gtadient echo row makes the phase place wraparound, in order to satisfy the CPMG condition.Usually, has orthogonal axes k _xAnd k _yRectangular coordinate system in the k space is described.In such description, along k _xAxle is used G _x, along k _yAxle is used G _yShould understand, other coordinate systems as polar coordinate system also can be used for describing the k space.

In Fig. 2 b illustration passing through of the spike train k space of causing.Because as mentioned above, for the first gtadient echo, G _yAmplitude be zero, so straight line b ₁K _yComponent is zero, so b1 is level.Then first pair turns to tip to turn to the next one (second) starting point on the straight line b2.Then second pair turns to tip to turn to the next one (the 3rd) starting point on the straight line b3.At last, the wraparound pulse is to turning back to the initial point in the k space.In being presented at Fig. 2 a, comprise G _x-G _yThe single spin echo interval of gtadient echo spike train is called as " fragment " in this article.

Change simultaneously phase encoding gradient G in each fragment by repeated fragment in pulse train _Pe(referring to Fig. 2 a), parallel but from b1 to b2 straight line such as the indication to b3 skew cause filling up three blades.Each repeated fragment causes not M the M bar straight line between the blade that be distributed on the same group.In Fig. 3 illustration each have gradient pulse row (G _xAnd G _yThe sequence of three spin echoes row).

For the fragment that repeats N time, N bar straight line will fill up each of M blade.For this scheme, excite (or TR) altogether to need to be evenly distributed on M between M the blade * N bar k space line at every turn, thereby compare with the FSE-PROPELLER with identical spin echo row length, with the data acquisition Speed improving M doubly.For desired matrix size L, the minimum number that excites P that covers the k space fully can be calculated by following formula:

$P=\frac{\mathrm{\π}}{2}\frac{L}{M\×N}---\left(1\right)$

The area of precipitous tip rather than only amplitude control how to finish the k space and pass through.Pass through for the k space of realizing being presented among Fig. 2 b, as shown in Figure 4, calculate the area that each turns to pip.These turn to the pip area to depend on the in succession rotational angle theta between the blade of the phase encoding amplitude of the spin echo of considering and two.Area (A below the particular phases encode gradient lobe _y) with the area corresponding with maximum phase coding step-length

Provide by following equation 2 and 3 respectively:

$A_y=\frac{e-0.5}{\mathrm{FOV}\×\mathrm{\γ}}---\left(2\right)$

$A_{y_{\max }}=\frac{E-0.5}{\mathrm{FOV}\×\mathrm{\γ}}---\left(3\right)$

Wherein FOV is the visual field take centimetre (cm) as unit, γ be gyromagnetic ratio (for proton spin, 42.58 * MHz/T), e is in the scope of-E+1≤e≤E, corresponding to the given phase encoding step-length in the blade, and E is corresponding to maximum positive phase coding step-length, by Interrelate with echo row length (M).Area A _yPositive sign or negative sign with place of depending on the phase encoding step.

Turning to based on being provided by equation 2 and 3 and using blade rotating angle θ along converting them the gradient area of respective components to reading with phase-encoding direction of rear blade between the blade.

In order to calculate the area that turns to pip required, need when the end of front vane and with the k space length between the head end of rear blade.For example, the k space length with

In (Fig. 4 b) corresponding situation, pass through and comprise from an e _B1Move to the top of blade b2.The required gradient area of this step is provided by equation 4.The gradient tip

Required area

Shown in equation 5, calculate.Strategy reaches the area that passes through and provided by equation 6 and 7 between blade b2 and the b3 like the application class

(for

) and

(for

).

$A_{y_{\mathrm{\θ}}}=(A_{y_{\max }}-A_y)+(A_{y_{\max }}+A_y)\cos \mathrm{\θ})---\left(4\right)$

$A_{x_{\mathrm{\θ}}}=-(A_{y_{\max }}+A_y)\sin \mathrm{\θ}---\left(5\right)$

$A_{y_{2\mathrm{\&theta;}}}=(A_{y_{\max }}-A_y)\cos \mathrm{\&theta;}-(A_{y_{\max }}+A_y)\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA00002673917600111.png"\; state="\{\{state\}\}">cos</figure-callout>}2\mathrm{\&theta;}---\left(6\right)$

$A_{x_{2\mathrm{\&theta;}}}=(A_{y_{\max }}-A_y)\sin \mathrm{\&theta;}+(A_{y_{\max }}+A_y)\sin 2\mathrm{\&theta;}---\left(7\right)$

From Fig. 4 b and 4c, can find out gradient

With

Have the negative polarity required such as their through direction.

Note, the gradient waveform that is presented in Fig. 2 a and 3 is incomplete.For example, not shown along G _xThe preset phase gradient of direction is because this gradient pulse is used exciting the RF pulse and again focus between the RF pulse usually.In addition, also omitted section and selected gradient, because in steering procedure, do not involve the section strobe pulse.It should be noted that G _xOr G _yLast gradient pulse in the fragment of spike train is important, and space orbit turns back to coherent location because it makes k-.

B. view ordering

Again between the focusing pulse, the spin echo amplitude is pressed T at each ₂The relaxation time decay.Consequently, near the straight line that the end of echo row, obtains, compare the SNR(signal to noise ratio (S/N ratio) with the straight line that early obtains) lower.Specify spin echo can between blade, cause large signal amplitude uncontinuity with form of straight lines, then cause the pseudo-shadow of serious ghost image.In the situation that Diffusion Imaging, the application of diffusion gradient causes with respect to the departing from of CPMG condition, causes phase place and amplitude in the odd number spin echo unstable.In order to compensate these impacts, can use view ordering as described below (as shown in Figure 5).The middle heart that strides across blade is specified the even number echo, so that the supercentral signal in k space is stable.Between blade edge, separate the odd number echo, and be designated as the T that strides across blade ₂There is not any rapid uncontinuity in attenuation distribution.

C. phase error and correction

Turn to-the PROP technology faces three kinds of needs and takes in order to obtain the phase error of the image that can accept quality.

1. between exciting: main by the phase place between the kinetic TR inconsistent (error);

2. between blade: stride across the phase place inconsistent (error) between the different gtadient echos that different leaves distributes; And

3. in the blade: cross the phase place inconsistent (error) of different k space lines for the fixed blade interior span.

Turn to-one of the advantage of PROP is separately to determine and independent ability of proofreading and correct above-mentioned three kinds of phase errors.The below provides further details.

Phase error in the blade

In order to obtain phase error in the blade, during prescan, use the GRASP pulse train with blade angle (that is, θ=0) to obtain two kinds of single-shot orthogonal reference scannings (ORS).In the first reference scan, use readout gradient along the x axle, and forbid all the gradient activities along the y axle.In the second reference scan, between x axle and y axle, scan gradient waveform.For every kind of reference scanning, the gtadient echo of all spin echoes of Fourier transform is to obtain the plural projection of object.From these projections, method computer memory constant (α) and linear (β) phase error (11) of using Ahn and Ch9 to propose:

Reference scan 1: α _1mn, β _1mn, m=1 ..., M blade, and n=1 ..., N bar straight line; And

Reference scan 2: α _2mn, β _2mn, m=1 ..., M blade, and n=1 ..., N bar straight line, wherein the first subscript represents reference scan number, and m and n represent respectively gtadient echo and spin echo index.For having angle of orientation φ _mGive fixed blade m, by following constant (ξ) and linearity (ψ) phase error of obtaining between the k space line:

ξ _mn=α _1mncosφ _m+α _2mnsinφ _m (8)

ψ _mn=β _1mncos ²φ _m+β _2mnsin ²φ _m. (9)

For known phase error, phase correction will set about by the gradient area of adjusting receiver frequency and fine setting the method for correcting phase of setting up being used for each blade in the blade.

Phase error between blade

Along with phase error in the blade is eliminated, can uses two kinds of means to proofread and correct and once excite phase error between interior blade.At first, can use phase place inconsistency between M the gtadient echo that from above-mentioned ORS, obtains.Can select the center gtadient echo of the first spin echo as a reference, and with respect to this phase error with reference to the every other gtadient echo of estimation.During rebuilding, use as the method for building up of EPI exploitation and eliminate constant and linear phase error (13).Secondly, can be by using phase error between phase estimation between the blade in more same the exciting of redundant data in the k space center district that all blades the pass through blade in once exciting.Then can during image reconstruction, eliminate the phase place inconsistency.This method is similar to Pipe(1) original propose that is a kind of, except only carrying out phase correction with each with same M the corresponding blade of each interior gtadient echo that excite, rather than use outside all PROPELLER blades.

Excite a phase error

A kinetic phase error that excites is by exciting the phase place between the group to proofread and correct according to the data consistency in the overlay region, center in k space is relatively more different.Pipe(1) algorithm that originally proposed for FSE-PROPELLER can be used for eliminating the phase error that excites of GRASP, except between the phase place of the different leaves group of from difference excites, obtaining, making comparisons, rather than outside making comparisons one by one blade.Both proofread and correct by this way in the plane and by the motion on plane.

In Fig. 6 illustration based on the example embodiment of the method for the turning to of k space-phase error correction that PRO passes through.For instance, this exemplary method can be the computer implemented method in above-mentioned MRI system the sort of.

As shown in Figure 6, in step 602, a GRASP sequence is applied to object in the MRI system.According to this example embodiment, a GRASP sequence can comprise the first radio frequency (RF) sequence of periodically RF pulse, along the periodicity G of first direction _xSpike train follow the first magnetic field gradient (G _x) sequence and along the periodicity G of second direction _ySpike train follow corresponding the first magnetic field gradient (G _y) sequence.By designing a RF, G according to above-mentioned steering technique _xAnd G _ySequence, they can be configured to make passing through along more than first parallel lines grouping in the k space, wherein each parallel lines grouping of more than first forms a corresponding GRASP blade, and each corresponding GRASP blade tilts with respect to other corresponding GRASP blades, and a GRASP blade corresponding to other intersects in the center in k space.

In step 604, with corresponding the first repetition interval of the duration of a GRASP pulse train (for example, excite for the first time) during therefrom obtain a GRASP k spatial data along more than first parallel lines grouping.

In step 606, the 2nd GRASP pulse train is used object in the MRI system, according to this example embodiment, the 2nd GRASP sequence can comprise the second radio frequency (RF) sequence of periodically RF pulse, along the periodicity G of first direction _xSpike train follow the second magnetic field gradient (G _x) sequence and along the periodicity G of second direction _ySpike train follow corresponding the second magnetic field gradient (G _y) sequence, by designing the 2nd RF, G according to above-mentioned steering technique _xAnd G _ySequence, they can be configured to make passing through along more than second parallel lines grouping in the k space, wherein each parallel lines grouping of more than second forms corresponding the 2nd GRASP blade, and each corresponding the 2nd GRASP blade tilts with respect to other corresponding the 2nd GRASP blades, and two GRASP blade corresponding to other intersects in the center in k space.

In step 608, with corresponding the second repetition interval of the duration of the 2nd GRASP pulse train (for example, excite for the second time) during therefrom obtain the 2nd GRASP k spatial data along more than second parallel lines grouping.

At last, in step 610, separately determine and independent phase calibration error: (i) k spatial data in the blade in the GRASPk spatial data, (ii) k spatial data between the blade in the GRASP k spatial data, (iii) k spatial data in the blade in the 2nd GRASP k spatial data, (iv) k spatial data between the blade in the 2nd GRASP k spatial data, and (excite a k spatial data between v) exciting for the first time and exciting for the second time.

Should understand, use turns to-and the phase error correction of PROP technology or GRASP sequence also can be embodied in the non-of short duration computer-readable medium as disk, CD-ROM etc., stored the non-of short duration computer-readable medium of computer executable program above comprising, if this computer executable program is carried out by one or several processor of MRI system, make the MRI system carry out the function of aforesaid exemplary method.Will also be appreciated that and can revise or rearrange above-mentioned method step, and add additional step, these do not change example embodiment or use and turn to-scope or the spirit of other embodiment of the phase error correction of PRO, for example, the above is described as right G _xAnd G _yPulse (comprise and turning to and the wraparound pulse) can need not strictly to use simultaneously.In certain embodiments, G _xAnd G _yThe designing institute official hour relation of spike train is to make paired pulse simultaneously approximate rather than simultaneously strict.

2. example operation and result

A. example procedure

At first turn to-the PROP sequence in the upper realization of 3.0T GE Signa HDx scanner (GE Healthcare, Waukesha, WI, USA) and test.FSE pulse train is modified as realization aforesaid turning to-PROP pulse train.This pulse train provides, uses the cylindrical GE DQA phantom scanner of quadrature head coil to test at first at MICROTEC.Utilizing following imaging parameters to obtain the T2 weighting in axial plane turns to-PROP image: TR=4s and TE=72ms.For the purpose of comparison, use traditional PROPELLER sequence and identical imaging parameters based on FSE to obtain similar image.

Through after this examining, a women volunteer of health (age: 29 years old) has been carried out several times experiment so that assessment turns to-the PROP sequence.All experiments all use the quadrature head coil to carry out.In volunteer's experiment first time, use following imaging parameters in brain, to obtain axial T2 and diffusion-weighted image: TR=4000ms, TE=128ms, ETL=8, matrix size=256, FOV=26cm, slice thickness=5mm, b=500s/mm ², NEX=2, and sweep time=2 minutes 13 seconds.In order to compare the correspondence image of also using FSE-PROPELLER also to obtain.Owing to usually using single-shot spin echo EPI to obtain the diffusion-weighted image, obtaining so utilize the coupling imaging parameters to carry out DW-EPI.

Turn in order to assess-PROP is to the robustness of subject motion, the volunteer is trained to lentamente mobile his head, in order to adjust at set intervals a lower frequency during obtaining.Obtaining on the similar section place with the front, the identical imaging parameters that utilization provides above obtains axially and turns to-PROP and FSE-PROPELLER image.Repeatedly exciting T2-weighting flute card FSE to obtain two kinds of acquisition strategies and standard compares.Subject's motion is equally matched in all three times scanning.

The dielectric resonance effect is usually more obvious high field is strong, causes the center of image obviously to brighten.Because this effect can make on 3.0T to turning to-evaluate complicated of PROP image, so also realize this pulse train at 1.5TGE Signa HDx scanner.For this pulse train, utilize quadrature to send-receive head coil and use following imaging parameters to obtain axially at 1.5T to turn to-PROP image: TR=4s TE=72ms, ETL=8, FOV=24cm, slice thickness=5mm, BW=125KHz, matrix size=256 * 256, and NEX=2.

Turn in order to show-robustness of PROP, further use following imaging parameters, obtain diffusion-weighted image: TR=4s on axial and non axial (that is, sagittal, the crown and inclination) plane on the volunteer, TE=72ms, ETL=8, FOV=24cm, slice thickness=5mm, BW=125KHz, matrix size=256 * 256, NEX=2, and b=500s/mm ²Clinoplane is chosen to parallel with tentorium cerebelli, with respect to approximately 40 ° of the axial planes on the volunteer.Utilize similar imaging parameters to obtain single-shot EPI image in the same place.

B. result

Fig. 7 shows the T of the phantom scanning of obtaining at 3T ₂-weighted image.Turn to-the PROP image (Fig. 7 b) to look that (Fig. 7 is a) equally matched with the FSE-PROPELLER image.The SNR measurement disclosed and turned to-and the PROP image compares with the FSE-RPOP image and reduced approximately 30%, but image taking speed is brought up to 3 times.

Figure 8 illustrates and utilize b=500s/mm ²And use EPI, FSE-PROPELLER and turn to-T that PROP obtains personage under test ₂-and the diffusion-weighted image.Turn to-picture quality (Fig. 8 c, f) of PROP and FSE-PROP(Fig. 8 b, e) picture quality equally matched.The main serious distortion EPI image (Fig. 8 a, d) is seen that is caused by the off-resonance effect as magnetic susceptibility turning to-the PROP image on be improved significantly.Because the dielectric resonance on the 3T, turning to-the PROP image in, observe shade at the rear side of brain.

Figure 9 illustrates and relatively use traditional F SE, FSE-PROPELLER and turn to-image of the performance of the exercise induced scanning of PROP sequence.Although FSE image (Fig. 9 a) show the relevant ghost image of serious motion, FSE-PROPELLER(Fig. 9 b) and turn to-PROP(Fig. 9 c) showing equally matchedly aspect the elimination motion artifacts.

Figure 10 shows what the 1.5T field intensity was obtained has a b=750s/mm ²T ₂-and the comparative result of diffusion-weighted image.Turn to-the PROP image (Figure 10 b, d) although slightly variant aspect contrast, demonstrate again and the equal picture quality of FSE-PROP image (Figure 10 a, c).Turn to-the PROP imagery exploitation combination T ₂And T ₂* weighting.T ₂* effect produces the contrast difference of observing.Compare with about 6 minutes of corresponding FSE-PROP, turn to-working time of PROP is about 2 minutes.It is further noted that to turn to-PROP do not demonstrate any dielectric shade on this field intensity.

At last, compare with traditional single-shot EPI, figure 11 illustrates the result to the turning to of the non axial diffusion-weighted scanning of personage under test-PROP sequence.Axial image (Figure 11 a, e) shows the minimum difference such as expection owing to the little magnetization rate variance in the specific imaging plane with from the less contribution of following gradient.For the image that obtains in the sagittal plane, because the localization distortion of following gradient fields and being caused by the magnetization rate variance in the frontal lobe, SS-EPI image (Figure 11 f) presents sizable overall distortion.Turn in correspondence-the PROP image and almost eliminated two types distortion in (Figure 11 b).In crown (Figure 11 c) and (Figure 11 d) plane that tilts, also observe similar improvement.

3. conclusion

Example embodiment of the present invention described above.But those of ordinary skill in the art should be understood that and can not depart from the scope and spirit of the present invention ground that limits such as claims to this embodiment change and modification.

List of references

(1)Pipe JG.Motion correction with PROPELLER MRI:application to headmotion and free-breathing cardiac imaging.Magn Reson Med 1999;42:963-969.

(2)Chuang TC,Huang TY，Lin FH,Wang FN,Juan CJ,Chung HW，Chen CY，Kwong KK.PROPELLER-EPI with parallel imaging using a circularly symmetricphased-array RF coil at 3.0 T:Application to high-resolution diffusion tensorimaging.Magnetic Resonance in Medicine 2006;56:1352-1358.

(3)Skare S,Newbould RD,Clayton DB,Bammer R.Propeller EPI in theother direction.Magnetic Resonance in Medicine 2006;55:1298-1307.

(4)Aldefeld B,B ornert P.Effects of gradient anisotropy in MRI.MagneticResonance in Medicine 1998;39:606-614.

(5)Zhou XJ,Maier JK.A new Nyquist ghost in oblique EPI.Proc Int'l SocMagn Reson Med 4th Meeting;New York,NY.p 386.1996.

(6)Zhou X,Maier JK,Epstein FH;Reduction of Nyquist ghost artifacts inoblique echo planar images.US patent 5,672,969.1997 September 30,1997.

(7)Reeder SB,Atalar E,Faranesh AZ,McVeigh ER.Referencelessinterleaved echo-planar imaging.Magnetic Resonance in Medicine1999;41:87-94.

(8)Pipe JG，Farthing VG，Forbes KP.Multishot diffusion-weighted FSE usingPROPELLER MRI.Magnetic Resonance in Medicine 2002;47:42-52.

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Claims (22)

1. computer implemented method in magnetic resonance imaging (MRI) system, it comprises:

With the object of the first radio frequency (RF) pulse application in the MRI system, and between the first fast spin echo (FSE) echo after the time interval, with the 2nd RF pulse application in this object;

During the time interval between the FSE echo between the first and second RF pulses along first direction with the first magnetic field gradient (G _x) spike train is applied to this object, a G _xSpike train comprises integer M adjacent G _xPulse, a G _xEvery couple of G in succession of spike train _xPulse is by G _xTurn to pulse separately, and a G _xThe last G of spike train _xThe pulse back is a G then _xThe wraparound pulse;

With a G _xSpike train side by side along second direction with the first magnetic field gradient (G _y) spike train is applied to this object, a G _ySpike train comprises M adjacent G _yPulse, a G _yEach G of spike train _yPulse and a G _xCorresponding G in the time of spike train _xThe corresponding first row G of pulse shaping _x-G _yPulse pair, a G _yEvery couple of G in succession of spike train _yPulse is by G _yTurn to pulse separately, this G _yTurn to pulse and a G _xCorresponding G in the time of spike train _xTurn to the corresponding first row G of pulse shaping _x-G _yTurn to pulse pair and a G _yThe last G of spike train _yThe pulse back is a G then _yThe wraparound pulse, a G _yWraparound pulse and a G _xThe one G of spike train _xWraparound pulse shaping first is G simultaneously _x-G _yWraparound pulse pair;

Obtain the k spatial data along the first group of mutual angled straight lines of M bar that intersects in the center in k space, each bar of first group the mutual angled straight lines of M bar is corresponding to different corresponding first row G _x-G _yPulse pair,

Wherein use each first row G _x-G _yTurn to pulse that starting point that the k space is passed through is reoriented to another from one of mutual angled straight lines of M bar of first group, and

Wherein use the first while G _x-G _yThe wraparound pulse is reoriented to the reference location in k space to the starting point that the k space is passed through.

2. the method for claim 1 further comprises:

Between the 2nd FSE echo after the 2nd RF pulse on the time interval with the 3rd RF pulse application in this object;

During the time interval between the 2nd FSE echo between the second and the 3rd RF pulse, will comprise M adjacent G _xThe 2nd G of pulse _xSpike train is applied to this object, the 2nd G _xEvery couple of G in succession of spike train _xPulse is by G _xTurn to pulse separately, and the 2nd G _xThe last G of spike train _xThe pulse back is the 2nd G then _xThe wraparound pulse;

With the 2nd G _xSpike train side by side will comprise M adjacent G _yThe 2nd G of pulse _ySpike train is applied to this object, the 2nd G _yEach G of spike train _yPulse and the 2nd G _xCorresponding G in the time of spike train _xThe corresponding secondary series G of pulse shaping _x-G _yPulse pair, the 2nd G _yEvery couple of G in succession of spike train _yPulse is by G _yTurn to pulse separately, this G _yTurn to pulse and the 2nd G _xCorresponding G in the time of spike train _xTurn to the corresponding secondary series G of pulse shaping _x-G _yTurn to pulse pair and the 2nd G _yThe last G of spike train _yThe pulse back is the 2nd G then _yThe wraparound pulse, the 2nd G _yWraparound pulse and the 2nd G _xThe 2nd G of spike train _xWraparound pulse shaping second is G simultaneously _x-G _yWraparound pulse pair;

Obtain the k spatial data along the second group of mutual angled straight lines of M bar that intersects in the center in k space, each bar of second group the mutual angled straight lines of M bar is corresponding to different corresponding secondary series G _x-G _yPulse pair,

Wherein each bar of second group the mutual angled straight lines of M bar and first group the mutual angled straight lines of M bar corresponding one parallel,

Wherein use each secondary series G _x-G _yTurn to pulse that starting point that the k space is passed through is reoriented to another from one of mutual angled straight lines of M bar of second group, and

Wherein use the second while G _x-G _yThe wraparound pulse is reoriented to the reference location in k space to the starting point that the k space is passed through.

3. the method for claim 1, wherein M is in the scope of 3-7.

4. the method for claim 1 is wherein used the first while G _x-G _yThe wraparound pulse is to making Carr-Purcell-Meiboom-Gill(CPMG) condition is met.

5. the method for claim 1 further is included in a G _xSpike train is before with initial a pair of G _xAnd G _yPulse application is in this object, in order to the reference location in k space is set.

6. the method for claim 1, wherein the reference location in k space is at the initial point in k space, and wherein the initial point in k space is the center in k space.

7. the method for claim 1, wherein roughly near the initial point in k space, wherein the initial point in k space is the center in k space to the reference location in k space.

8. the method for claim 1 further is included in a RF pulse and will initially excites the RF pulse application in this object before,

Wherein the first and second RF pulses are again to focus on the RF pulse.

9. computer implemented method in magnetic resonance imaging (MRI) system, it comprises:

The first gradient and spin echo screw propeller (GRASP) pulse train are applied to object in the MRI system, and this first gradient and spin echo screw propeller (GRASP) pulse train comprises the first radio frequency (RF) sequence of periodically RF pulse, along the periodicity G of first direction _xSpike train follow the first magnetic field gradient (G _x) sequence and along the periodicity G of second direction _ySpike train follow corresponding the first magnetic field gradient (G _y) sequence, a RF, G _xAnd G _ySequence is configured to make passing through along more than first parallel lines grouping in the k space, each parallel lines grouping of more than first forms a corresponding GRASP blade, and each corresponding GRASP blade tilts with respect to other corresponding GRASP blades, and a GRASP blade corresponding to other intersects in the center in k space;

During first repetition interval corresponding with the duration of a GRASP pulse train, therefrom obtain a GRASP k spatial data along more than first parallel lines grouping;

The 2nd GRASP pulse train is applied to this object, and the 2nd GRASP pulse train comprises the 2nd RF sequence, the periodicity G of periodically RF pulse _xSpike train follow the 2nd G _xSequence and periodicity G _ySpike train follow corresponding the 2nd G _ySequence, the 2nd RF, G _xAnd G _ySequence is configured to make passing through along more than second parallel lines grouping in the k space, each parallel lines grouping of more than second forms corresponding the 2nd GRASP blade, and each corresponding the 2nd GRASP blade tilts with respect to other corresponding the 2nd GRASP blades, and two GRASP blade corresponding to other intersects in the center in k space;

During second repetition interval corresponding with the duration of the 2nd GRASP pulse train, therefrom obtain the 2nd GRASP k spatial data along more than second parallel lines grouping; And

Separately determine and independent the correction:

(i) phase error in the GRASPk spatial data that obtains between the parallel lines of each corresponding GRASP blade,

Phase error in the GRASP k spatial data that (ii) obtains between the corresponding GRASP blade,

(iii) phase error in the 2nd GRASPk spatial data that obtains between the parallel lines of each corresponding the 2nd GRASP blade,

Phase error in the 2nd GRASP k spatial data that (iv) obtains between corresponding the 2nd GRASP blade, and

(the phase error in a GRASP who v) obtains between a GRASP pulse train and the 2nd GRASP pulse train and the 2nd GRASP k spatial data.

10. method as claimed in claim 9 further comprises:

The 3rd GRASP pulse train is applied to this object, and the 3rd GRASP pulse train comprises the 3rd RF sequence, the periodicity G of periodically RF pulse _xSpike train follow the 3rd G _xSequence and periodicity G _ySpike train follow corresponding the 3rd G _ySequence, the 3rd RF, G _xAnd G _ySequence is configured to make passing through along more than the 3rd parallel lines grouping in the k space, each parallel lines grouping of more than the 3rd forms corresponding the 3rd GRASP blade, and each corresponding the 3rd GRASP blade tilts with respect to other corresponding the 3rd GRASP blades, and three GRASP blade corresponding to other intersects in the center in k space;

During the three repetition time interval corresponding with the duration of the 3rd GRASP pulse train, therefrom obtain the 3rd GRASP k spatial data along more than the 3rd parallel lines grouping; And

Separately determine and independent the correction:

(i) phase error in the 3rd GRASPk spatial data that obtains between the parallel lines of each corresponding the 3rd GRASP blade,

Phase error in the 3rd GRASP k spatial data that (ii) obtains between corresponding the 3rd GRASP blade, and

Phase error in a GRASP, the 2nd GRASP that (iii) obtains between a GRASP pulse train, the 2nd GRASP pulse train and the 3rd GRASP pulse train and the 3rd GRASP k spatial data.

11. method as claimed in claim 9, wherein a G _xSequence comprises an Integer N periodicity G _xSpike train, and a G _ySequence comprises N corresponding periodically G _ySpike train,

A G wherein _xEach of sequence be G periodically _xSpike train comprises an integer M G _xPulse, and a G _yEach of sequence be G periodically _ySpike train comprises M corresponding G _yPulse,

A G wherein _xEach of sequence be G periodically _xThe M of a spike train G _xEach of pulse and a G _yThe corresponding one-period G of sequence _yThe M of a spike train G _yOne of the correspondence of pulse is used simultaneously,

Wherein more than first comprises and M M the parallel lines grouping that a GRASP blade is corresponding, and

Wherein each GRASP blade comprises the N bar parallel lines that pass through in the k-space.

12. method as claimed in claim 11, wherein M in [3,7] scope and N in [4,64] scope.

13. method as claimed in claim 9 further comprises:

Before a RF sequence, excite the RF pulse application in this object with first; And

Before the 2nd RF sequence, excite the RF pulse application in this object with second,

Wherein periodically the First ray of RF pulse comprises the First ray that again focuses on the RF pulse, and

Wherein periodically the second sequence of RF pulse comprises the second sequence that again focuses on the RF pulse.

14. method as claimed in claim 11, wherein separately definite and independent phase error of proofreading and correct in the GRASP k spatial data that obtains between the parallel lines of each corresponding GRASP blade comprises:

Will be identical with a GRASP pulse train but do not have a G _yFirst of the blade that sequence and can not causing mutually tilts is applied to this object with reference to GRASP pulse train;

Obtaining first with reference to GRASP k spatial data with first with reference to the first corresponding interim reference time of the duration of GRASP pulse train, this first comprises M G of the parallel reference line of N bar of k spatial data with reference to GRASP k spatial data corresponding to each _xWith reference to blade;

Will be identical with a GRASP pulse train but do not have a G _xSecond of the blade that sequence and can not causing mutually tilts is applied to this object with reference to GRASP pulse train;

Obtaining second with reference to GRASP k spatial data with second with reference to the second corresponding interim reference time of the duration of GRASP pulse train, this second comprises M G of the parallel reference line of N bar of k spatial data with reference to GRASP k spatial data corresponding to each _yWith reference to blade;

By calculating the first Fourier transform with reference to GRASP k spatial data, from obtain first with reference to determining the GRASP k spatial data respectively and M G _xThe corresponding space stationary phase error alpha of each bar with reference to the N bar parallel lines of the k spatial data in each of blade _1mnWith space linear phase error β _1mn, m=1 ..., M, and n=1 ..., N;

By calculating the second Fourier transform with reference to GRASP k spatial data, from obtain second with reference to determining the GRASP k spatial data respectively and M G _yThe corresponding space stationary phase error alpha of each bar with reference to the N bar parallel lines of the k spatial data in each of blade _2mnWith space linear phase error β _2mn, m=1 ..., M, and n=1 ..., N;

Be that each bars of the N bar parallel lines in each of a M GRASP blade is determined space stationary phase error ξ by calculating following formula _MnWith space linear phase error ψ _Mn:

ξ _Mn=α _1mnCos φ _m+ α _2mnSin φ _m, and

ψ _mn=β _1mncos ²φ _m+β _2mnsin ²φ _m，

φ wherein _mIt is the angle of orientation of a m GRASP blade in the k space;

Determine the phase error correction corresponding with each the k spatial data of each bar of N bar parallel lines of a M GRASP blade, so that the definite space stationary phase error ξ of compensation _MnWith space linear phase error ψ _MnAnd

Each the k spatial data of each bar of N bar parallel lines to a M GRASP blade is used the phase error correction of determining.

15. method as claimed in claim 14, wherein separately definite and independent phase error of proofreading and correct in the GRASP k spatial data that obtains between the corresponding GRASP blade comprises:

More than first and second each particular vane with reference to blade are arranged to reference between blade;

Determine more than first and second with reference to each estimating phase error with respect to reference between blade of the rest blade of blade; And

To be applied to a GRASP k spatial data from more than first and second estimating phase errors with reference to blade.

16. method as claimed in claim 15, wherein the 2nd G _xSequence comprises N periodically G _xSpike train, and the 2nd G _ySequence comprises N corresponding periodically G _ySpike train,

The 2nd G wherein _xEach of sequence be G periodically _xSpike train comprises M G _xPulse, and the 2nd G _yEach of sequence be G periodically _ySpike train comprises M G _yPulse,

The 2nd G wherein _xEach of sequence be G periodically _xThe M of a spike train G _xEach of pulse and the 2nd G _yThe corresponding one-period G of sequence _yThe M of a spike train G _yOne of the correspondence of pulse is used simultaneously,

Wherein more than second comprises and M M the parallel lines grouping that the 2nd GRASP blade is corresponding,

Wherein each the 2nd GRASP blade comprises the N bar parallel lines that pass through in the k-space, and

The phase error of wherein separately determining and independently proofreading and correct in the 2nd GRASP k spatial data that obtains between the parallel lines of each corresponding the 2nd GRASP blade comprises:

Be that each bars of the N bar parallel lines in each of M the 2nd GRASP blade is determined space stationary phase error ξ by calculating following formula _MnWith space linear phase error ψ _Mn

ξ _Mn=α _1mnCos φ _m+ α _2mnSin φ _m, and

ψ _mn=β _1mncos ²φ _m+β _2mnsin ²φ _m，

φ wherein _mIt is the angle of orientation of m the 2nd GRASP blade in the k space;

Determine the phase error correction corresponding with each the k spatial data of each bar of N bar parallel lines of M the 2nd GRASP blade, so that the definite space stationary phase error ξ of compensation _MnWith space linear phase error ψ _MnAnd

Each the k spatial data of each bar of N bar parallel lines to M the 2nd GRASP blade is used the phase error correction of determining.

17. method as claimed in claim 16, wherein separately definite and independent phase error of proofreading and correct in the 2nd GRASP k spatial data that obtains between corresponding the 2nd GRASP blade comprises:

To be applied to the 2nd GRASP k spatial data from more than first and second estimating phase errors with reference to blade.

18. method as claimed in claim 17, a GRASP who wherein separately obtains between definite and independent correction the one GRASP pulse train and the 2nd GRASP pulse train and the phase error in the 2nd GRASP k spatial data comprise:

(i) compared from the first center k spatial data of the corresponding part in the center with the k space of a GRASP blade and (ii) the second center k spatial data with the corresponding part in the identical central district in k space from the 2nd GRASP blade;

According to the phase place inconsistency between relative discern the first center k spatial data and the second center k spatial data; And

Phase correction is applied to a GRASP k spatial data and the 2nd GRASP k spatial data in order to eliminate the phase place inconsistency of identifying

19. a magnetic resonance imaging (MRI) system, it comprises:

One or more processors;

Storer;

Main magnet;

Be placed on a plurality of gradient coils in this main magnet;

The RF transceiver system;

The RF coil block;

Signal is sent to the pulse module of this RF coil block;

Be subjected to the RF switch of this pulse module control; And

Be stored in the machine readable instructions in this storer, this machine readable instructions makes this MRI system realize comprising following function when being carried out by these one or more processors:

With the object of the first radio frequency (RF) pulse application in this MRI system, and between the first fast spin echo (FSE) echo after the time interval, with the 2nd RF pulse application in this object;

During the time interval between the FSE echo between the first and second RF pulses along first direction with the first magnetic field gradient (G _x) spike train is applied to this object, a G _xSpike train comprises integer M adjacent G _xPulse, a G _xEvery couple of G in succession of spike train _xPulse is by G _xTurn to pulse separately, and a G _xThe last G of spike train _xThe pulse back is a G then _xThe wraparound pulse;

With a G _xSpike train side by side along second direction with the first magnetic field gradient (G _y) spike train is applied to this object, a G _ySpike train comprises M adjacent G _yPulse, a G _yEach G of spike train _yPulse and a G _xCorresponding G in the time of spike train _xThe corresponding first row G of pulse shaping _x-G _yPulse pair, a G _yEvery couple of G in succession of spike train _yPulse is by G _yTurn to pulse separately, this G _yTurn to pulse and a G _xCorresponding G in the time of spike train _xTurn to the corresponding first row G of pulse shaping _x-G _yTurn to pulse pair and a G _yThe last G of spike train _yThe pulse back is a G then _yThe wraparound pulse, a G _yWraparound pulse and a G _xThe one G of spike train _xWraparound pulse shaping first is G simultaneously _x-G _yWraparound pulse pair;

Obtain the k spatial data along the first group of mutual angled straight lines of M bar that intersects in the center in k space, each bar of first group the mutual angled straight lines of M bar is corresponding to the corresponding first row G of difference _x-G _yPulse pair,

Wherein use each first row G _x-G _yTurn to pulse that starting point that the k space is passed through is reoriented to another from one of mutual angled straight lines of M bar of first group, and

Wherein use the first while G _x-G _yThe wraparound pulse is reoriented to the reference location in k space to the starting point that the k space is passed through.

20. a magnetic resonance imaging (MRI) system wherein comprises:

One or more processors;

Storer;

Main magnet;

Be placed on a plurality of gradient coils in this main magnet;

The RF transceiver system;

The RF coil block;

Signal is sent to the pulse module of this RF coil block;

Be subjected to the RF switch of this pulse module control; And

Be stored in the machine readable instructions in this storer, this machine readable instructions makes this MRI system realize comprising following function when being carried out by these one or more processors:

The first gradient and spin echo screw propeller (GRASP) pulse train are applied to object in the MRI system, and this first gradient and spin echo screw propeller (GRASP) pulse train comprises the first radio frequency (RF) sequence of periodically RF pulse, along the periodicity G of first direction _xSpike train follow the first magnetic field gradient (G _x) sequence and along the periodicity G of second direction _ySpike train follow corresponding the first magnetic field gradient (G _y) sequence, a RF, G _xAnd G _ySequence is configured to make passing through along more than first parallel lines grouping in the k space, each parallel lines grouping of more than first forms a corresponding GRASP blade, and each corresponding GRASP blade tilts with respect to other corresponding GRASP blades, and a GRASP blade corresponding to other intersects in the center in k space;

A GRASP k spatial data is therefrom obtained in parallel lines grouping along more than first during first repetition interval corresponding with the duration of a GRASP pulse train;

The 2nd GRASP pulse train is applied to this object, and the 2nd GRASP pulse train comprises the 2nd RF sequence, the periodicity G of periodically RF pulse _xSpike train follow the 2nd G _xSequence and periodicity G _ySpike train follow corresponding the 2nd G _ySequence, the 2nd RF, G _xAnd G _ySequence is configured to make passing through along more than second parallel lines grouping in the k space, each parallel lines grouping of more than second forms corresponding the 2nd GRASP blade, and each corresponding the 2nd GRASP blade tilts with respect to other corresponding the 2nd GRASP blades, and two GRASP blade corresponding to other intersects in the center in k space;

The 2nd GRASP k spatial data is therefrom obtained in parallel lines grouping along more than second during second repetition interval corresponding with the duration of the 2nd GRASP pulse train; And

Separately determine and independent the correction:

(i) phase error in the GRASPk spatial data that obtains between the parallel lines of each corresponding GRASP blade,

Phase error in the GRASP k spatial data that (ii) obtains between the corresponding GRASP blade,

(iii) phase error in the 2nd GRASPk spatial data that obtains between the parallel lines of each corresponding the 2nd GRASP blade,

Phase error in the 2nd GRASP k spatial data that (iv) obtains between corresponding the 2nd GRASP blade, and

(the phase error in a GRASP who v) obtains between a GRASP pulse train and the 2nd GRASP pulse train and the 2nd GRASP k spatial data.

21. one kind contains the non-of short duration computer-readable medium of storing superincumbent instruction, this instruction is in case by one or more processors execution of magnetic resonance imaging (MRI) system, just make this MRI system realize comprising following function:

With the object of the first radio frequency (RF) pulse application in this MRI system, and between the first fast spin echo (FSE) echo after the time interval, with the 2nd RF pulse application in this object;

During the time interval between the FSE echo between the first and second RF pulses along first direction with the first magnetic field gradient (G _x) spike train is applied to this object, a G _xSpike train comprises integer M adjacent G _xPulse, a G _xEvery couple of G in succession of spike train _xPulse is by G _xTurn to pulse separately, and a G _xThe last G of spike train _xThe pulse back is a G then _xThe wraparound pulse;

With a G _xSpike train side by side along second direction with the first magnetic field gradient (G _y) spike train is applied to this object, a G _ySpike train comprises M adjacent G _yPulse, a G _yEach G of spike train _yPulse and a G _xCorresponding G in the time of spike train _xThe corresponding first row G of pulse shaping _x-G _yPulse pair, a G _yEvery couple of G in succession of spike train _yPulse is by G _yTurn to pulse separately, this G _yTurn to pulse and a G _xCorresponding G in the time of spike train _xTurn to the corresponding first row G of pulse shaping _x-G _yTurn to pulse pair and a G _yThe last G of spike train _yThe pulse back is a G then _yThe wraparound pulse, a G _yWraparound pulse and a G _xThe one G of spike train _xWraparound pulse shaping first is G simultaneously _x-G _yWraparound pulse pair;

Obtain the k spatial data along the first group of mutual angled straight lines of M bar that intersects in the center in k space, each bar of first group the mutual angled straight lines of M bar is corresponding to the corresponding first row G of difference _x-G _yPulse pair,

Wherein use each first row G _x-G _yTurn to pulse that starting point that the k space is passed through is reoriented to another from one of mutual angled straight lines of M bar of first group, and

Wherein use the first while G _x-G _yThe wraparound pulse is reoriented to the reference location in k space to the starting point that the k space is passed through.

22. one kind contains the non-of short duration computer-readable medium of storing superincumbent instruction, this instruction is in case by one or more processors execution of magnetic resonance imaging (MRI) system, just make this MRI system realize comprising following function:

The first gradient and spin echo screw propeller (GRASP) pulse train are applied to object in the MRI system, and this first gradient and spin echo screw propeller (GRASP) pulse train comprises the first radio frequency (RF) sequence of periodically RF pulse, along the periodicity G of first direction _xSpike train follow the first magnetic field gradient (G _x) sequence and along the periodicity G of second direction _ySpike train follow corresponding the first magnetic field gradient (G _y) sequence, a RF, G _xAnd G _ySequence is configured to make passing through along more than first parallel lines grouping in the k space, each parallel lines grouping of more than first forms a corresponding GRASP blade, and each corresponding GRASP blade tilts with respect to other corresponding GRASP blades, and a GRASP blade corresponding to other intersects in the center in k space;

A GRASP k spatial data is therefrom obtained in parallel lines grouping along more than first during first repetition interval corresponding with the duration of a GRASP pulse train;

The 2nd GRASP pulse train is applied to this object, and the 2nd GRASP pulse train comprises the 2nd RF sequence, the periodicity G of periodically RF pulse _xSpike train follow the 2nd G _xSequence and periodicity G _ySpike train follow corresponding the 2nd G _ySequence, the 2nd RF, G _xAnd G _ySequence is configured to make passing through along more than second parallel lines grouping in the k space, each parallel lines grouping of more than second forms corresponding the 2nd GRASP blade, and each corresponding the 2nd GRASP blade tilts with respect to other corresponding the 2nd GRASP blades, and two GRASP blade corresponding to other intersects in the center in k space;

The 2nd GRASP k spatial data is therefrom obtained in parallel lines grouping along more than second during second repetition interval corresponding with the duration of the 2nd GRASP pulse train; And

Separately determine and independent the correction:

(i) phase error in the GRASPk spatial data that obtains between the parallel lines of each corresponding GRASP blade,

Phase error in the GRASP k spatial data that (ii) obtains between the corresponding GRASP blade,

(iii) phase error in the 2nd GRASPk spatial data that obtains between the parallel lines of each corresponding the 2nd GRASP blade,

Phase error in the 2nd GRASP k spatial data that (iv) obtains between corresponding the 2nd GRASP blade, and

(the phase error in a GRASP who v) obtains between a GRASP pulse train and the 2nd GRASP pulse train and the 2nd GRASP k spatial data.

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